1. Technical Field
The invention relates to text input technology. More specifically, the invention relates to text entry solutions to wireless communication devices which have limited keypads.
2. Description of the Prior Art
For many years, portable computers have been getting smaller and smaller. The principal size-limiting component in the effort to produce a smaller portable computer has been the keyboard. If standard typewriter-size keys are used, the portable computer must be at least as large as the keyboard. Miniature keyboards have been used on portable computers, but the miniature keyboard keys have been found to be too small to be easily or quickly manipulated by a user. Incorporating a full-size keyboard in a portable computer also hinders true portable use of the computer. Most portable computers cannot be operated without placing the computer on a flat work surface to allow the user to type with both hands. A user cannot easily use a portable computer while standing or moving.
Presently, a tremendous growth in the wireless industry has spawned reliable, convenient, and very popular mobile devices available to the average consumer, such as cell phones, PDAs, MP3 players, etc. Handheld wireless communications and computing devices requiring text input are becoming smaller still. Further, advances in portable wireless technologies have led to a demand for small and portable two-way messaging systems, both SMS and e-mail, and for mobile Web browsing. Wireless communications device manufacturers also desire to provide devices which the consumer can operate with the same hand that is holding the device.
Disambiguation Background
Prior development work has considered use of a keyboard that has a reduced number of keys. As suggested by the keypad layout of a touch-tone telephone, many of the reduced keyboards have used a 3-by-4 array of keys. Each key in the array of keys contains multiple characters. There is therefore ambiguity as a user enters a sequence of keys, because each keystroke may indicate one of several letters. Several approaches have been suggested for resolving the ambiguity of the keystroke sequence, referred to as disambiguation.
One suggested approach for unambiguously specifying characters entered on a reduced keyboard requires the user to enter, on average, two or more keystrokes to specify each letter. The keystrokes may be entered either simultaneously (chording) or in sequence (multiple-stroke specification). Neither chording nor multiple-stroke specification has produced a keyboard having adequate simplicity and efficiency of use. Multiple-stroke specification is inefficient, and chording is complicated to learn and use.
Other suggested approaches for determining the correct character sequence that corresponds to an ambiguous keystroke sequence are summarized in Arnott, Probabilistic Character Disambiguation for Reduced Keyboards Using Small Text Samples, Journal of the International Society for Augmentative and Alternative Communication Arnott and M. Y. Javad (hereinafter the “Arnott article”). The Arnott article notes that the majority of disambiguation approaches employ known statistics of character sequences in the relevant language to resolve character ambiguity in a given context. The article also references research on word-based disambiguation systems and their respective advantages and disadvantages.
T9® Text Input is the leading commercial product offering word-level disambiguation for reduced keyboards, as taught in U.S. Pat. No. 5,818,437 and subsequent patents. Ordering the ambiguous words by frequency of use reduces the efficiency problems identified by previous research, and the ability to add new words makes it even easier to use over time. Input sequences may be interpreted simultaneously as words, word stems, and/or completions, numbers, and unambiguous character strings based on stylus tap location or keying patterns, such as multi-tap.
Another commonly used keyboard for small devices consists of a touch-sensitive panel on which some type of keyboard overlay has been printed, or a touch-sensitive screen with a keyboard overlay displayed. Depending on the size and nature of the specific keyboard, either a finger or a stylus can be used to interact with the panel or display screen in the area associated with the key or letter that the user intends to activate. Due to the reduced size of many portable devices, a stylus is often used to attain sufficient accuracy in activating each intended key.
The system described in U.S. Pat. No. 6,801,190 uses word-level auto-correction to resolve the accuracy problem and permit rapid entry on small keyboards. Because tap locations are presumed to be inaccurate, there is some ambiguity as to what the user intended to type. The user is presented with one or more interpretations of each keystroke sequence corresponding to a word, such that the user can easily select the desired interpretation. This approach enables the system to use the information contained in the entire sequence of keystrokes to resolve what the user's intention was for each character of the sequence.
Handwriting recognition is another approach that has been taken to solve the text input problem on small devices that have a touch-sensitive screen or pad that detects motion of a finger or stylus. Writing on the touch-sensitive panel or display screen generates a stream of data input indicating the contact points. The handwriting recognition software analyzes the geometric characteristics of the stream of data input to determine each character or word. Due to differences in individual writing styles and the limitations of handwriting technology on mobile devices, however, recognition accuracy is less than perfect, resulting in character ambiguity even though current handwriting systems do not typically reveal that ambiguity to the user.
A Need for Improvements to Current Disambiguation Methodologies
A specific challenge facing word-based disambiguation is that of providing sufficient feedback to the user about the keystrokes being input, particularly for the novice or infrequent user who is unfamiliar with the reduced keyboard layout or the disambiguation system. With an ordinary typewriter or word processor, each keystroke represents a unique character which can be displayed to the user as soon as it is entered. But with word-level disambiguation, for example, this is often not possible, because each entry represents multiple characters, and any sequence of entries may match multiple words or word stems. The ambiguity may confuse the first-time user if the system displays characters that change as each key is pressed: the user does not know that the system offers the desired word at the end, and he may needlessly attempt to fix each character before proceeding. Ambiguity is especially a problem when, for example, the user makes a spelling or entry error and is not aware of such error until the complete sequence is entered and the desired result is not presented. Displaying word stems that match the partial sequence reduces this problem, by showing when the user is on the right track towards the desired word, but does not eliminate it entirely, especially if some stems are concealed due to display space constraints.
U.S. Pat. No. 5,818,437 describes a keystroke window (102) that displays keycap icons representing the ambiguous key sequence, which confirms that the user pressed the intended keys. But the display provides neither an explanation of how the words are being assembled from that key sequence nor feedback that the user is on the right track.
Moreover, some alphabets, such as Thai and Arabic, contain more letters than the alphabet for English, which leads to even greater ambiguity on a reduced number of keys. Efficient and confident input of these languages demands a mechanism for reducing the appearance of that ambiguity when needed.